1. Field of Invention
This invention relates to video decoders, and in particular to video decoder having a comb filter system that utilizes host memory.
2. Related Art
The complexity and flexibility of electronic processing devices such as personal computers (“PCs”), personal digital assistants (“PDAs”), two-way set top boxes (both for cable and satellite), personal video recorders (“PVRs”), cellular telephones, two-way pagers, and other host devices capable of processing information are growing a rapid pace. As such, these types of devices have become common place in today's society.
With the growth, improvement, and general acceptance of the Internet, more information is becoming accessible to these types of devices in varying forms of content leading to a fusion between these types of devices and various types of multimedia content. As an example, the growth of both cable and satellite type television systems has resulted in cable ready televisions, two-way set top boxes (the devices that interface between the cable or satellite systems and the television monitor generally known as “STBs”), digital cable, cable modems to access the Internet, Internet based web-TV, digital telephone over cable, on-demand video services, etc. Additionally, devices such as cable ready televisions, web-TVs, Internet capable video games, and PCs are increasing being connected to either cable or satellite type broadband systems to enable broadband connectivity with the Internet.
As an example, as PCs become more multimedia type devices, video and audio content are becoming important for PC users. Radio and television tuner add-on devices from numerous vendors are common place. Generally, these radio and/or television tuner add-on devices are peripheral devices that include an audio, video, or both, decoder (i.e., an audio/video decoder—also know generically as a “A/V decoder” and/or “video decoder”) that is capable of receiving a broadcast composite video signal (i.e., having luminance and chrominance spectra components, also known as channels) that is transmitted in one of the world's three television transmission formats (i.e., either NTSC, PAL, or SEACAM) and converts it to a digital data stream component video signal (i.e., having red, green, and blue “RGB” or “Y PbPr”) that has a format that is readable to the particular type of PC. Luminance (“Y”) describes a black and white image in full detail and chrominance (“C” also referred to as “UV”) describes coloration of the image. These types of video decoders may vary in the way they separate luminance and chrominance spectra in the composite video signal and generally include either a notch filter or comb filter.
In the case of video decoders utilizing a comb filter, the comb filter separates the composite video signal into both Y and C channels to reduce both cross-luma (i.e., cross-luminance) and cross-chroma (i.e., cross-chrominance) artifacts. The comb filter is utilized so that the resulting video images show fine picture detail from standard broadcasts, Laserdisk, and other composite sources. Video decoders utilizing a comb filters also reduce discolorations in fine picture detail and provide purer color overall.
In general, known video decoders utilize three-line (“3-line”) adaptive comb filters (also known as three-line two-dimensional “3-line 2D” comb filters) or higher quality three-dimensional (“3D”) comb filters (also know as “3D Y/C filter,” “3D digital comb filter,” or “motion adaptive” comb filters). As far as 3D comb filters, in addition to separating the Y and C channels of a composite video signal, a 3D comb filter also performs two additional functions. While comparing three consecutive horizontal scan lines within a single video frame, the 3D comb filter also analyzes each frame for improved image quality.
Unfortunately, known approaches to 3D comb filtering of composite video typically requires local memory frame buffers (on the video decoder) to hold the previous frames of video for use in the 3D comb filter. As a result, currently known peripheral devices utilizing 3D comb filters (such as, for example, PC TV 3D comb filter cards) have an additional standalone integrated circuit (“IC”) along with a dedicated dynamic read access memory (“DRAM”) to provide frame buffer storage of previous video fields required for the 3D comb filter. This additional hardware adds significant cost and complexity to the peripheral device and as peripheral devices move towards dual-tuner use, board space for all of the required additional components on the peripheral device also becomes an issue.
Therefore, there is a need for a new comb filter system on a peripheral device that does not require the utilization of dedicated DRAM on the peripheral device.